1. Field of the Invention
The present invention relates to an apparatus for testing the film or seal integrity of pouches which contain flowable materials.
2. Description of the Related Art
It is well known to package flowable materials, for example, milk, on so-called vertical form and fill machines. Using such a machine, a flat web of synthetic thermoplastic film is unwound from a roll and formed into a continuous tube in a tube forming section, by sealing the longitudinal edges of the film together to form a so-called lap seal or a so-called fin seal. The tube thus formed is pulled vertically downwards to a filling station. The tube is then collapsed across a transverse cross-section of the tube, the position of the cross-section being at a sealing device below the filling station. A transverse heat seal is made, by the sealing device, at the collapsed portion of the tube, thus making an airtight seal across the tube. The sealing device generally comprises a pair of jaws. After making the transverse seal, but before the jaws of the sealing device are opened, a quantity of material to be packaged, e.g. liquid, is caused to enter the tube, at the filling station, and fill the tube upwardly from the aforementioned transverse seal. The tube is then caused to move downwardly a predetermined distance. Such movement may be under the influence of the weight of the material in the tube, or may be caused by pulling or mechanically driving the tube. The jaws of the sealing device are closed again, thus collapsing the tube at a second transverse section. The second transverse section may be above, usually just above, the air/material interface in the tube, or the second transverse section may be below the air/material interface. The sealing device seals and severs the tube transversely at the second transverse section. The material-filled portion of the tube is now in the form of a pillow shaped pouch. Thus the sealing device has sealed the top of the filled pouch, sealed the bottom of the next-to-be formed pouch, all in one operation. One such vertical form and fill machine of the type described above is sold under the trade mark PREPAC. With some other machines, the sealing device does not sever the tube at the second transverse section, but does sever the tube subsequently. The portions of the pouch at the ends of the transverse seals are often referred to as "ears".
For many years, milk has been packaged in pouches made on vertical form and fill machines. Such pouches have been sold to household consumers and, in use, such milk-filled pouches are stood within an open-mouthed pitcher. More recently, such pouches have been used to package other flowable comestibles, mayonnaise, salad dressings, preserves and the like. Pouches containing such comestibles are usually sold to "institutional" buyers, e.g. restaurants.
It is also known to package flowable materials in sachets which have seals around three or four sides of the sachet. Such sachets may contain portion-sized comestibles such as mustard, ketchup, sugar and the like. In the context of the present invention the term "sachet" is intended to come within the scope of the term "pouch".
Heretofore, the integrity of pouch seals has been tested by a number of methods. One entails dropping a number of pouches from a given height onto a hard floor. This method suffers from the disadvantage that after one drop of the pouch from a given height, the pouch may be weakened, and further drops from greater heights, until the pouch bursts or leaks, may not be truly indicative of the pouch's integrity. As used herein the term "integrity" means the ability of the pouch to remain whole, i.e. without leakage of material from inside the pouch. Another method involves squeezing and twisting the pouch by hand. Such a test is highly subjective and depends on the person doing the test. One commercially available pouch tester allows air pressure to be applied to the inside of the pouch via a needle inserted in the pouch. The air pressure is monitored by a pressure gauge connected to another needle inserted in the pouch. A major disadvantage of this tester is that the pouch integrity is destroyed by insertion of a needle into the pouch. Another commercially available tester places a pouch under vacuum inside a dome. This tester takes time to generate the high vacuum required and is therefore not very convenient. Another method of testing pouches which is more convenient and reliable is desired. Furthermore an apparatus which is portable would be very desirable.